Wrong Position From cvGoodFeaturesToTrack()!

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Hi, All

We are trying to locate corners with cvGoodFeaturesToTrack. The version is opencv 2.3.1. The test picture is a 24-bit bmp file, which is manually made with Windows Pen. So you know, it is a "perfect" picture. It has no noise.

There is only one inner corner in the picture. It looks like BMW logo.

And this is the code:

cvGoodFeaturesToTrack(pGrayImg,
  OUT pEigImg, 
  OUT pTempImg, 
  OUT sCorners, 
  IN &iAmtCorners, //corner_count
  0.0510, //quality_level
  5.0, //min_distance
  0, //mask
  15, //block_size
  0, //use_harris
  0.04); //k CV_DEFAULT(0.04)

The code told me that the corner lies in (101, 60). However, it should be (94, 67). We drew a circle at (101, 60) and we found it doesn't overlap the corner! Why the function returns a wrong position?

Thanks!